Currently, a communications system generally uses different types of reference signals: one type of reference signal is used to estimate a channel, so as to perform coherent demodulation on a received signal that includes control or data information; another type of reference signal is used for a channel state/channel quality measurement, so as to implement scheduling, or implement selection of a cell, a transmitting point, or a receiving point, or the like.
For example, in a downlink system of long term evolution (LTE) R10 developed by the 3rd generation partnership project (3GPP), a reference signal used for coherent demodulation is called a demodulation reference signal (DMRS), where the DMRS is also called a user equipment (UE)-specific reference signal; and a reference signal used for channel state information measurement is called a channel state information reference signal (CSI-RS). The DMRS is sent together with data of a physical downlink shared channel (PDSCH) and used for channel estimation during PDSCH demodulation. The CSI-RS can be used by a UE in an R10 system to measure a channel state, especially for a multi-antenna transmission situation. A rank indicator (RI)/a precoding matrix indicator (PMI)/a channel quality indicator (CQI), and other feedback information can be exported based on the CSI-RS channel measurement. In addition, a cell-specific reference signal (CRS) can be used by a UE to estimate a channel, so as to perform demodulation on a physical downlink control channel (PDCCH) and another common channel, where the reference signal is inherited from an LTE R8/9 system. The CRS is also used for channel state information measurement and data channel demodulation in the LTE R8/9 system. In LTE R8-R11 systems, the CRS is also used for signal quality information measurement, so as to implement selection of a cell, a transmitting point, or a receiving point.
In addition, in an LTE R11 system, the DMRS in LTE R10 supports a maximum of eight antenna ports, where a quantity of DMRS antenna ports that is used by each UE depends on scheduling, and scheduling information may be notified to each UE by using downlink control information (DCI). The CSI-RS in LTE R10 supports a maximum of eight antenna ports, where a quantity of antenna ports may be one, two, four, or eight. The CRS in LTE R8R10 supports a maximum of four antenna ports, where a quantity of antenna ports may be one, two, or four.
During the research and practice of the prior art, the inventor of the present application finds that the existing LTE R10 supports a maximum of only eight antenna ports; as communications traffic increases, eight antenna ports cannot meet a requirement in some scenarios.